How do I achieve a bending effect with the collision of two rectangles?
Here is a way to do it with the Mesh Deform modifier:


Create your block A, subdivide it, give it a Subdivision Surface modifier.
Create a second block, B, with the same kind of subdivision, and that contains A. No modifier for this one, but in the Properties panel > Object > Display > Choose Draw All Edges and Maximum Display > Wire. Now B should only show its wire.
Also, for B, in Object mode, in the Properties panel > Data > Shape Keys, create a first one, called Basis by default, then create a second one.
Give A a Mesh Deform modifier, put it above the Subdivision Surface modifier, choose B as the Object, and click Bind.
Select B, make sure that the second Shape Key is selected, go in Edit mode, and change the shape of the mesh as you want. A should be deformed.
Now animate as you want (study how the Shape Keys are running if you don't know enough about it).